Simple sugar concentration sensor and method

ABSTRACT

A glucose sensor comprising an optical energy source having an emitter with an emission pattern; a first polarizer intersecting the emission pattern; a second polarizer spaced a distance from the first polarizer and intersecting the emission pattern, the second polarizer rotated relative to the first polarizer by a first rotational amount Θ; a first optical detector intersecting the emission pattern; a second optical detector positioned proximal to the second polarizer, the first polarizer and the second polarizer being positioned between the optical energy source and the second optical detector, the second optical detector intersecting the emission pattern; a compensating circuit coupled to the second optical detector; and a subtractor circuit coupled to the compensating circuit and the first optical detector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of U.S. patent application Ser. No. 16/031,026, filed Jul. 10, 2018, which is a continuation of U.S. patent application Ser. No. 15/582,264, filed on Apr. 28, 2017, now U.S. Pat. No. 10,067,054, which is a continuation-in-part of and claims the benefit of U.S. patent application Ser. No. 15/093,547, filed on Apr. 7, 2016, now U.S. Pat. No. 9,636,052, which is a continuation of and claims the benefit of U.S. patent application Ser. No. 14/822,524 filed Aug. 10, 2015, now U.S. Pat. No. 9,320,463, which is a continuation and claims the benefit of U.S. patent application Ser. No. 14/293,356 filed Jun. 2, 2014, now U.S. Pat. No. 9,101,308, which is a continuation and claims the benefit of U.S. patent application Ser. No. 13/950,054 filed Jul. 24, 2013, now U.S. Pat. No. 8,743,355, which claims the benefit of U.S. Provisional Patent Application No. 61/714,731, filed Oct. 16, 2012; all of which are incorporated herein by reference in their entirety.

STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to monitoring of simple sugar (or monosaccharide) content within a fluid. More specifically, the invention uses an optical energy source in combination with polarizers to determine the change in a sugar level (e.g., glucose) of a subject fluid relative to a baseline concentration, such as blood.

2. Description of the Related Art

Simple sugar changes the polarization of the optical energy passing through it according to the equation Θ=α×L×C, where L is the travel length of the energy through the fluid in which the sugar is concentrated, C is the sugar concentration, and α is a constant that depends on the type of sugar, wavelength of the energy, and the fluid. If L and α are known, by measuring the change in polarization of energy passing through a sugar-containing fluid relative to a baseline measurement, the sugar concentration of the fluid can be derived.

This principle may be used, for example, to non-invasively determine the glucose concentration of human blood. Normal blood has a non-zero glucose concentration C, which causes a change in polarization for energy passing through the blood. For a glucose concentration of 70 mg/dL and an α=45.62 (×10⁻⁶) degrees/mm/(mg/dL), energy of wavelength 633 nm and a 3.0 mm path length will have a rotation Θ of 0.00958 degrees. Measuring the change in rotation caused by the sugar allows derivation of the current sugar concentration.

SUMMARY OF THE INVENTION

The present invention may be used to monitor sugar (e.g., glucose) in a fluid, and provides numerous advantages over traditional techniques that rely on a standard polarization analyzer, which requires actively moving parts and angular resolution precision to 0.01 degrees. First, the present invention is non-invasive, which lowers the risk of contamination. Second, the present invention may provide an ability to stream real-time, continuous data. Third, the present invention provides a low operating cost.

The invention includes an optical energy source having an emitter with an emission pattern; a first polarizer intersecting the emission pattern; a second polarizer spaced a distance from the first polarizer and intersecting the emission pattern, the second polarizer rotated relative to the first polarizer by a first rotational amount Θ; a first optical detector intersecting the emission pattern; a second optical detector positioned proximal to the second polarizer, the first polarizer and the second polarizer being positioned between the optical energy source and the second optical detector, the second optical detector intersecting the emission pattern; a compensating circuit coupled to the second optical detector; and a subtractor circuit coupled to the compensating circuit and the first optical detector.

In one or more embodiments is described an apparatus for measuring change in sugar concentration in a fluid relative to a baseline concentration. The apparatus comprises a source of optical energy, said source having an emitter having an emission pattern. The apparatus comprises a first optical detector spaced a distance from said source. The apparatus comprises a second optical detector collocated with said first optical detector. The apparatus comprises a plurality of polarizers optically between said source and said detectors. The plurality of polarizers comprises a first polarizer intersecting the emission pattern. The plurality of polarizers comprises a second polarizer rotated relative to the first polarizer by a first rotational amount Θ, spaced a distance from the first polarizer, and proximal to said second optical detector, wherein said first polarizer is optically between said source and said second polarizer. With the apparatus, the distance between the first and second polarizers is sufficient to enable the optical positioning of a volume of liquid intersecting said emission pattern between said first polarizer and said second polarizer and optically between the first polarizer and the first detector. The apparatus comprises at least one circuit coupled to said first optical detector and said second optical detector. The at least one circuit comprises a compensating circuit coupled to said second optical detector, a subtractor circuit coupled to said compensating circuit and said first optical detector, and a gain circuit coupled to said subtractor circuit. With the apparatus, in one or more embodiments, the at least one circuit further comprises a unity gain circuit coupled to and between said first optical detector and said subtractor circuit. With the apparatus, in one or more embodiments, the Θ is 45.028 degrees. With the apparatus, in one or more embodiments, the optical energy source is a near-infrared wavelength optical energy source. With the apparatus, in one or more embodiments, the optical energy source is a red-wavelength energy source. With the apparatus, in one or more embodiments, the optical energy source is a LED. With the apparatus, in one or more embodiments, the optical energy source is a laser. With the apparatus, in one or more embodiments, the fluid is blood. With the apparatus, in one or more embodiments, the apparatus further comprises a form factor wearable around an ear, said form factor housing the optical energy source, the first polarizer, the second polarizer, the first optical detector, and the second optical detector. With the apparatus, in one or more embodiments, the Θ is between thirty-five and fifty-five degrees (inclusive) of rotation from a baseline rotation caused by a baseline concentration of a simple sugar in a fluid for energy traveling a length L through said fluid. With the apparatus, in one or more embodiments, the Θ is between forty and fifty degrees (inclusive). With the apparatus, in one or more embodiments, the Θ is forty-five degrees. With the apparatus, in one or more embodiments, the plurality of polarizers consists of said first polarizer and said second polarizer. With the apparatus, in one or more embodiments, the optical energy is unmodulated. With the apparatus, in one or more embodiments, the optical energy consists of one unmodulated light wave.

In one or more embodiments described herein is method of detecting an amount of change of sugar concentration in a subject fluid relative to a baseline concentration. The method comprises directing optical energy in a first direction. The method comprises positioning the subject fluid between a first polarizer and a first detector, between said first polarizer and a second polarizer rotated relative to the first polarizer by a first rotational amount Θ, and between said first polarizer and a second detector, wherein said second polarizer is positioned between the first polarizer and said second detector. The method comprises passing the optical energy through the first polarizer to become once-polarized optical energy. The method comprises passing the once-polarized optical energy through the subject fluid to become rotated once-polarized optical energy. The method comprises detecting an intensity of the rotated once-polarized optical energy. The method comprises passing at least a portion of the rotated once-polarized optical energy through the second polarizer to become twice-polarized optical energy. The method comprises detecting the intensity of the twice-polarized optical energy. The method comprises providing a signal representative of a difference between the intensity of the rotated once-polarized optical energy and the intensity of the twice-polarized optical energy. The method comprises correlating the signal to a sugar concentration. With the method, in one or more embodiments, the optical energy is red-wavelength optical energy. With the method, in one or more embodiments, the optical energy is near-infrared optical energy. With the method, in one or more embodiments, the first optical detector is collocated with said second optical detector.

In one or more embodiments is a system for measuring a change in polarization of energy across a fluid. The system comprises a single source for emitting energy. The system includes a first polarizer for polarizing the energy emitted from the source to provide a first polarized energy. The system includes a second polarizer for polarizing at least a portion of the first polarized energy and to provide a second polarized energy, wherein the second polarizer is rotated by a rotational amount with respect to the first polarizer. The system includes a first detector for detecting the first polarized energy received a distance away from the first polarizer. The system includes a second detector for detecting the second polarized energy. The system includes a module coupled with the first detector and the second detector, the module comprising a first unit for receiving output from the first detector and a second unit for receiving output from the second detector, the module comparing the first and second outputs. With the system, in one or more embodiments, the first unit of the module comprises an attenuator for reducing at least a portion of the output from the first detector. With the system, in one or more embodiments, the second unit of the module comprises a compensator for boosting at least a portion of the output from the second detector. With the system, in one or more embodiments, the system comprises a subtractor for reducing at least a portion of the output from the first detector. With the system, in one or more embodiments, the energy is in the form of light emitted in a near infrared frequency range. With the system, in one or more embodiments, the polarizer is selected from a film, wire grid, holographic wire grid, and beamsplitter. With the system, in one or more embodiments, the second polarizer is rotated by a rotational amount that is at least about 45 degrees or a multiple of about 45 degrees. With the system, in one or more embodiments, the system further comprises a signal amplifier for amplifying output from the module. With the system, in one or more embodiments, the system is fitted to an ear such that the first polarizer is on a first facing surface of an ear while the second polarizer, the first detector, the second detector and the module are on an opposing second facing surface of the ear.

In one or more embodiments is a system for measuring a change in polarization of energy across a portion of a human body part. The system comprises a first polarizer for polarizing energy emitted from a source and to provide a first polarized energy to a first facing surface of the human body part. The system comprises a second polarizer for polarizing at least a portion of the first polarized energy received from the first polarizer when positioned on a second opposing facing surface of the human body part. The system comprises a first detector for detecting at least a portion of the first polarized energy when received on the second opposing facing surface of the human body part. The system comprises a second detector for detecting at least a portion of the second polarized energy when received on the second opposing facing surface of the human body part. The system comprises a module operably coupled the first detector and the second detector on the second opposing facing surface of the human body part. The module comprises a first unit for receiving output from the first detector and a second unit for receiving output from the second detector. The module utilizes the outputs from the first and second units to derive a glucose concentration. With the system, in one or more embodiments, the second polarizer is rotated by a rotational amount with respect to the first polarizer. With the system, in one or more embodiments, the rotational amount is between and includes 35 degrees and 55 degrees. With the system, in one or more embodiments, the system further comprises at least a first band pass filter to filter the output from the first detector and a second band pass filter to filter the output from the second detector.

Still further is described an apparatus for measuring change in sugar concentration in a subject fluid. The apparatus comprises a source of energy, the source having an emitter with an emission pattern. The apparatus comprises a first detector spaced a distance from the source. The apparatus comprises a second detector collocated with said first detector. The apparatus comprises a plurality of polarizers between the source and the detectors. The plurality of polarizers comprise at least a first polarizer intersecting the emission pattern. The plurality of polarizers comprise at least a second polarizer rotated relative to the first polarizer by a first rotational amount Θ, spaced a distance from the first polarizer, and proximal to said second detector, wherein the first polarizer is between the source and the second polarizer. With the apparatus, in one or more embodiments, the distance between the first polarizer and the second polarizer enables the positioning of a volume of liquid intersecting the emission pattern between the first polarizer and the second polarizer and optically between the first polarizer and the first detector. With the apparatus, in one or more embodiments, the apparatus further comprising at least one circuit coupled to the first detector and the second detector. With the apparatus, the at least one circuit comprises a compensating circuit coupled to the second detector, a subtractor circuit coupled to the compensating circuit and said first detector, and a gain circuit coupled to said subcontractor circuit. With the apparatus, in one or more embodiments, the compensating circuit comprises a unity gain circuit coupled to and between the second detector and the subtractor circuit. With the apparatus, in one or more embodiments, the compensating circuit comprises an attenuator coupled to and between first detector and the subtractor circuit. With the apparatus, in one or more embodiments, the plurality of polarizers consists of the first polarizer and the second polarizer. With the apparatus, in one or more embodiments, the energy is unmodulated. With the apparatus, in one or more embodiments, the energy source is a LED. With the apparatus, in one or more embodiments, the Θ is between thirty-five and fifty-five degrees inclusive of rotation from a baseline rotation caused by a baseline concentration of a simple sugar in a fluid for energy traveling a length L through said fluid. With the apparatus, in one or more embodiments, the Θ is between forty and fifty degrees inclusive.

An apparatus for measuring change in sugar concentration in a fluid relative to a baseline concentration is also described herein. The apparatus comprises a source of energy, said source having an emitter with an emission pattern. The apparatus comprises a first detector spaced a distance from said source. The apparatus comprises a second detector collocated with said first detector. The apparatus comprises a first polarizer intersecting the emission pattern. The apparatus comprises a second polarizer rotated relative to the first polarizer by a first rotational amount Θ, spaced a distance from the first polarizer, and proximal to said second detector, wherein said first polarizer is optically between said source and said second polarizer. The apparatus comprises a volume of liquid, said volume intersecting said emission pattern and positioned between said first polarizer and said second polarizer and between said first polarizer and said first detector. The apparatus comprises at least one circuit coupled to said first detector and said second detector. The at least one circuit comprises a compensating circuit coupled to said second detector. The at least one circuit comprises a subtractor circuit coupled to said compensating circuit and said first detector. The at least one circuit comprises a gain circuit coupled to said subtractor circuit.

As mentioned, a noninvasive system for measuring glucose is provided and discussed above. The system may further include a feedback circuit connecting the light source and the first detector and configured to adjust the intensity of the light capable of penetrating body tissue to maintain the at least some or all of the first polarized light detected by the first detector within a first portion calibration range.

In various instances, the first portion calibration range is defined by an upper calibration threshold greater than a first target intensity value and a lower calibration threshold lesser than a first target intensity value.

Also as discussed, a method for measuring glucose is provided. In various instances, the method also includes providing a feedback circuit connecting the light source and the first detector and configured to adjust the intensity of the light capable of penetrating body tissue to maintain the at least some or all of the first polarized light detected by the first detector within a first portion calibration range.

Yet additionally mentioned, a method for measuring glucose is provided. This method may also provide for adjusting the intensity of the light emitting from the light source by a feedback circuit connecting the light source and the first detector, and in response to the first output, wherein the adjusting maintains the first output within a first portion calibration range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a system diagram of an embodiment of the invention.

FIG. 1B is a system diagram of an embodiment of the invention including an feedback aspect.

FIG. 2A is a circuit diagram of the circuit described with reference to FIG. 1A.

FIG. 2B is a circuit diagram of the circuit described with reference to FIG. 1B.

FIG. 3A is the system diagram of FIG. 1A showing the embodiment in use with a human ear.

FIG. 3B is the system diagram of FIG. 1B showing the embodiment in use with a human ear.

FIG. 4A-4C show actual data from an embodiment of the present invention used to derive sugar concentrations for three separate cases.

FIG. 5A-5C show the same data shown in FIGS. 4A-4C in a different form, with the unpolarized and polarized waveforms imposed on one another

FIG. 6A-C shows data from an embodiment of the present invention demonstrating the effect of the feedback aspect according to FIGS. 1B, 2B, and 3B.

DESCRIPTION OF THE VARIOUS EMBODIMENTS

FIGS. 1A-B show an embodiment 20 of the invention, which comprises an optical energy source 22, a first polarizer 24, a second polarizer 26 spaced a distance from the first polarizer 24 having a rotation Θ relative to the first polarizer 24, a first optical energy detector 28, a second optical energy detector 30 collocated with the first detector 28, and a circuit 46. Each of the first and second optical detectors 28, 30 are oriented to receive optical energy passing through a space 32. In the preferred embodiment, the detectors 28, 30 are silicon detectors. As used herein, “collocated” means being positioned adjacent each other so that, all else being equal, light from a common source will enter each of the detectors with approximately equal intensity. In addition, although the embodiment discloses the use of silicon detectors, other types of detectors may be used (e.g., photoresistors). As shown in FIG. 1B, in various instances, a feedback circuit 101 interconnects the optical energy source 22 and the first optical energy detector 28, although in yet further instances, the feedback circuit 101 may interconnect the optical energy source 22 and the second optical energy detector 30. The feedback circuit 101 operates to adjust the source optical energy magnitude of the optical energy from the optical energy source 22 in response to the energy of the optical energy received at the first optical energy detector 28, or in yet further instances, the second optical energy detector 30.

When actuated, the energy source 22 produces initial optical energy 34 having an emission pattern 36. The energy source 22 is preferably a red light source, such as a red light-emitting diode (LED) or a laser, but may alternatively be near-infrared. Ultimately, the initial optical energy 34 must be of a wavelength that may be affected by the presence of sugar in the subject fluid while also passing through the other vessel in which the fluid is contained. The initial optical energy 34 from the optical energy source 22 has a magnitude termed the source optical energy magnitude.

The first polarizer 24 is positioned proximal to the source 22, such that the initial optical energy 34 passes through the first polarizer 24 and becomes polarized energy 38. The polarized energy 38 traverses the space 32 between the first and second polarizer 24, 26, where a first portion 40 of the polarized energy 38 is detected by a first optical detector 28 and a second portion 42 of the polarized energy 38 passes through a second polarizer 26 to the second optical energy detector 30. Notably, first detector and second detector 28, 30 are collocated, despite the proximity of second polarizer 26 to the second detector 30. Because the space 32 is empty in FIG. 1, the polarized energy 38 passing through the space 32 is not rotated by, for example, the presence of a sugar in a fluid.

Preferably, the first and second polarizers 24, 26 are a linearly-polarized film because such film is inexpensive compared to other available alternatives. Such film, however, is optimal for energy wavelengths in the visible spectrum. Other polarizers may be used, provided that the selected wavelength of the energy source 22 is chosen to optimally correspond. For example, an alternative polarizer may be wire-grid or holographic, which is optimally configured for use in the present invention with energy of near-infrared and infrared wavelengths.

In various embodiments, the first and second polarizers 24, 26 each comprise a keying notch. A keying notch may comprise a cutout of the polarizer that corresponds to a tab in a housing. In various embodiments, the keying notch and/or tab may be positioned to establish a difference in rotation between the polarizers 24, 26. Moreover, in various instances, the first and second polarizers 24, 26 are a linearly-polarized film prepared by CNC cutting. Consequently, in various embodiments, the linearly-polarized film may have a keying notch prepared by CNC cutting.

Preferably, the difference in rotation between the polarizers 24, 26 is forty-five degrees (or an integral multiple of forty-five degrees) plus the rotation caused by the baseline. In this optimal case, a change in concentration relative to the baseline at least initially moves along the most linear portion of a sine wave, which makes detecting the change in rotation easier compared to moving further away from where the slope of the wave is 1 and further towards where the slope is 0 (i.e., the crest and troughs of the sine wave). For example, when used with a baseline glucose concentration 100 mg/dL over a length of L, Θ equals 0.014 degrees. In this case, the rotation between the polarizers should be 45.014 degrees. The greater the change in concentration from the baseline, however, the more non-linear the correlation of the rotation to the change in concentration.

The first and second detectors 28, 30 are electrically coupled to the circuit 46. The circuit 46 has a compensating circuit 48, a subtractor circuit 50, and a gain circuit 52. The first detector 28 is directly coupled to the subtractor circuit 50. The second detector 30 is coupled to the compensating circuit 48, which boosts the gain of the signal produced by the second detector 30 by an amount sufficient to compensate for the loss of intensity attributable to the portion 42 of polarized energy 38 passing through the polarized film and the effects of polarization due to the baseline concentrations in the fluid, but the compensating circuit 48 does not compensate for the loss in intensity resulting from changes in polarization due to the concentration change from some baseline itself. The subtractor circuit 50 produces a signal that is the difference between the signals received from the first and second detectors 28, 30. The gain circuit 52 amplifies the signal to a usable level.

Notably, in alternative embodiments, the compensating circuit 48 may be an attenuator coupled to the first detector 28 to equalize the intensity of the received optical energy, with the objective being that the difference in energy seen by the first detector 28 and the second detector 30 relates to the rotation of the energy rather than its amplitude. Similarly, the subtractor circuit 50 may be replaced by a Wheatstone or similar bridge.

In further embodiments, the circuit 46 is configured to integrate numerical model improvements to increase stability and consistent response to glucose via a feedback aspect, such as an open loop feedback method. Thus, as shown in FIG. 1B, a feedback circuit 101 may be included as an aspect of circuit 46 and as explained above. For example, in various instances the circuit 46 would primarily involve coupling the amount of transmitted light detected at the reference detector, such as a first detector 28, and adjusting the LED drive current provided to the optical energy source 22 to maintain a constant detected amplitude at the first detector 28. The ability to control optical energy source 22, and more specifically, the LED associated with the optical energy source will fall in a range of capability of the LED driver circuit. A further aspect also implemented in this embodiment involves aspects to address an observed ‘roll-off’ identified at high range glucose values. The artifacts may be predicted to be based in a combination of specific component parts choices such as may develop through tolerance stack up or nominal value drift. As such, the circuit 46 may include offset correction that allow for correction for both photodiodes and amplified components. By maintaining a constant detected amplitude at the first detector 28, a change in concentration relative to the baseline may be more accurately and precisely detected as the change at least initially moves along the most linear portion of the sine wave, because the maintaining of a constant detected amplitude compensates for common mode path attenuation and/or differential mode path attenuation, arising from inconsistencies in the placement of the optical energy source 34 and/or first detector 28 and/or second detector 30 relative to a tissue under test, such as a human ear tissue (see FIG. 3B).

Attenuation of the light may flatten the slope of the line comparing the differential intensity/polarization of the light at the first detector 28 and/or second detector 30 to the amount of glucose in the blood of the tissue under test. By implementing a feedback circuit 101 to maintain the intensity of the light at or near a target value at one of the detectors (such as first detector 28), the relationship of glucose in the blood to differential intensity/polarization of the light at the first detector 28 and/or second detector 30 may more accurately be measured by maintaining the intensity within a known region of the response curve. Moreover, the circuit 46 may implement a computational model wherein the bulk tissue scattering of the light passing through the tissue may be considered to include three components: (1) bulk attenuation (optical power loss) which is compensated by the feedback, (2) unpolarized transmitted light (scattered light), and (3) polarized light (ballistic photon fraction).

Referring to FIG. 2A, the outputs of the first and second detectors 28, 30 are provided to the circuit 46. The circuit 46 comprises the compensating circuit 48 having a potentiometer Ro1, the subtractor circuit 50, first and second 30-Hz low pass filters that included Ro1 and C1, and Ro2 and C2, and the gain circuit 52. The subtractor circuit 50 and the gain circuit 52 incorporate an OPA 211KP operational amplifier IC 66. The low pass filters reject any noise at the detectors 28, 30. Polarized output 53 and the unpolarized outputs 55 are fed to the subtractor circuit 50, which comprises Ro3, Ro4, R13 and R14. The subtractor circuit output 54 is then provided to the gain circuit 52 comprising Ro5 and C3. The final signal is provided at the gain circuit output 56. The embodiment includes an optional unity gain circuit 57 for phase-matching purposes. In various embodiments, all or a portion of circuit 46 and/or compensating circuit 48 comprises an application-specific integrated circuit (ASIC). For instance, multiple components may be packaged as a single integrated circuit, enabling further miniaturization of the circuit 46.

Referring to FIG. 2B further example embodiments of circuit 40 including the feedback circuit 101 are depicted. Referring to FIG. 2A and FIG. 2B, the operation of the feedback circuit 101 of FIG. 2B would be akin to (with reference to FIG. 2A) maintaining a constant optical detected power on first detector 28 (e.g., the detector receiving light passing through polarizer 24 rather than the detector receiving light passing through both polarizers 24 and 30). Changes in power to first detector 28 would result in a signal altering the supplied optical energy incident on the total detection system from an optical source 22 (LED, laser, and/or similar source), not shown in FIG. 2A.

FIGS. 3A-B show the embodiment 20 in use with a human ear 68, at least a portion of which occupies the space 32. The preferred orientation of the ear 68 within the space 32 is so that the polarized energy 38 passes through the ear 68 generally parallel to a lateral axis, where L is the distance along the axis of the measured fluid. For most human ears, L is approximately three millimeters of capillary-rich and blood vessel-rich skin.

When actuated, the energy source 22 produces initial optical energy 34 having the emission pattern 36. The initial energy 34 passes through the first polarizer 24, and is of a wavelength to which the non-sugar components of the ear 68 (i.e., skin, blood, tissue, cartilage) are, to at least some extent, transparent.

After passing through the first polarizer 24, the initial energy 34 becomes polarized energy 38. Glucose within the blood in the ear 68, however, will cause a change in polarization of the energy 38 according to Θ=α×L×C, causing the rotated energy 70 exiting the ear to have a first rotation Θ₁.

The intensity of a first portion 72 of the rotated energy 70 is detected by the first detector 28. The intensity of a second portion 74 of the rotated energy 70 passes through the second polarizer 26 and is detected by the second detector 30. Each of the first and second detectors 28, 30 produces a signal representative of the received intensity. Because the intensity of the rotated energy 70 received by the second detector 30 is only the intensity of the rotated energy component passing through the second polarizer 26, by measuring the difference in intensities at the detectors 28, 30, the rotation caused by the glucose in the ear 70 can be derived, from which the changed in glucose concentration relative to a baseline can be determined.

To determine the baseline, prior to use, the embodiment 20 is calibrated to a baseline glucose concentration of seventy mg/dL (a “normal” concentration for human blood) by changing a potentiometer, such as potentiometer 60 (FIG. 2A) to compensate for the difference in intensities of energy received by the first and second detectors 28, 30. Thus, any change in measured rotation represents a change in glucose concentration from some baseline (e.g., 70 mg/dL).

An alternative embodiment of the invention is calibrated to a baseline glucose concentration of 100 mg/dL using wavelength of 650 nm, resulting in a rotation of 45.028 degrees of the second polarizer relative to the first polarizer. This results range of resulting rotation of the baseline plus or minus 0.2 degrees for a glucose concentration of between 30 mg/dL and 300 mg/dL. Thus, a glucose concentration of 30 mg/dL will result in a rotational difference between the detectors of 0.0096 degrees, whereas a glucose concentration of 300 mg/dL will result in a rotational difference of 0.0273 degrees in the opposite direction of the direction of the 30 mg/dL concentration.

With specific reference to FIG. 3B in combination with FIG. 2B, notably, and differently from the discussion with reference to FIG. 2A and FIG. 3A above, a feedback circuit 101 conveys a feedback signal from first detector 28 to the energy source 22 producing initial optical energy 34. The feedback circuit 101 adjusts the energy source 22 to maintain the first portion 72 of the rotated energy within a first portion calibration range. More specifically, in response to the energy of the intensity of the first portion 72 of the rotated energy 70 deviating below a lower calibration threshold from a first target intensity value, the feedback signal directs the energy source 22 to increase the intensity of the initial optical energy 34 (source optical energy magnitude) until the intensity of the first portion 72 of the rotated energy 70 no longer falls below a lower calibration threshold from a first target intensity value. Similarly, in response to the intensity of the first portion 72 of the rotated energy 70 deviating above an upper calibration threshold from a first target intensity value, the feedback signal directs the energy source 22 to decrease the intensity of the initial optical energy 34 (source optical energy magnitude) until the intensity of the first portion 72 of the rotated energy 70 no longer is above the upper calibration threshold from the first target intensity value. The upper calibration threshold and the lower calibration threshold define the boundaries of the first portion calibration range.

While the difference between the intensity of the first portion 72 and the second portion 74 of the rotated energy is measured similarly to as discussed above, the intensity of the first portion 72 is maintained between the upper calibration threshold and the lower calibration threshold about the first target intensity value. Because the optical transmissivity of the ear 70 changes exponentially with the tissue thickness, and yet the difference in intensity of the first portion 72 and second portion 74 relates to the glucose concentration according to a linear approximation, relatively small changes in tissue thickness can result in relatively large shifts along a numerical approximation curve, causing calculation errors. Consequently the feedback mechanism discussed herein maintains the comparison within the same or similar linear region of the approximation curve, aiding calculation accuracy.

As previously mentioned, to determine the baseline, prior to use, the embodiment 20 is calibrated to a baseline glucose concentration of seventy mg/dL (a “normal” concentration for human blood) by changing a potentiometer, such as potentiometer 60 (FIG. 2A) to compensate for the difference in intensities of energy received by the first and second detectors 28, 30. Thus, any change in measured rotation represents a change in glucose concentration from some baseline (e.g., 70 mg/dL).

An alternative embodiment of the invention is calibrated to a baseline glucose concentration of 100 mg/dL using wavelength of 650 nm, resulting in a rotation of 45.028 degrees of the second polarizer relative to the first polarizer. This results range of resulting rotation of the baseline plus or minus 0.2 degrees for a glucose concentration of between 30 mg/dL and 300 mg/dL. Thus, a glucose concentration of 30 mg/dL will result in a rotational difference between the detectors of 0.0096 degrees, whereas a glucose concentration of 300 mg/dL will result in a rotational difference of 0.0273 degrees in the opposite direction of the direction of the 30 mg/dL concentration.

Notably, in various instances the feedback circuit 101 operates so that the determined baseline may be further adjusted to compensate for variations in the intensity of the first portion 72 of the rotated energy 70 detected by the first detector 28 and/or the intensity of the second portion 74 of the rotated energy 70 passed through the second polarizer 26 and detected by the second detector 30. For instance, variations in placement of the human ear 68 at least a portion of which occupies the space 32 may cause variations in the intensity of the first portion 72 and/or the intensity of the second portion 74. As such, in various instances, a feedback circuit 101 of the circuit 46 may cause the intensity of the first portion 72 or the intensity of the second portion 74 to be returned to at or near the determined baseline regardless of the relative inconsistency of positioning on the human ear 68. As a result, the rotation caused by the glucose in the ear 70 can be derived. As mentioned, because the intensity of the rotated energy 70 received by the second detector 30 is only the intensity of the rotated energy component passing through the second polarizer 26, by measuring the difference in intensities at the detectors 28, 30, the rotation caused by the glucose in the ear 70 can be derived, from which the changed in glucose concentration relative to a baseline can be determined.

Rather than changing the potentiometer 60 to compensate for the difference in intensities of energy received by the first and second detectors 28, 30 to calibrate the embodiment 20 to a baseline glucose concentration of seventy mg/dL (a “normal” concentration for human blood), instead, the device may actively implement feedback via the feedback circuit 101 to continuously or intermittently recalibrate so that any change in measured rotation represents a change in glucose concentration from some baseline (e.g., 70 mg/dL). By controlling feedback circuit 101, the circuit 46 may learn compensation offset values and may store these values in a memory rather than requiring the changing of the potentiometer 60. In this manner the feedback circuit 101 may operate to account for circuit variations and allow recalibration of the relationship between measured rotation and change in glucose concentration from a base line. In this manner, the feedback circuit 101 may operate so that the slope intercept calculations may remain unhampered by the exponential effect on photon transmissivity of the ear 70 (and associated exponential effect on intensity of detected light) that is caused by a linear change in a thickness of ear 70. Thus the feedback circuit 101 may be multipurpose.

In various instances, there are at least two methods for calibrating the invention. First and preferably, during fabrication of each sensor, a sample control serum or a similar component that would rotate the polarization state a known amount would be inserted in the space. This control would provide a simulated known glucose concentration for use in adjusting the device to the proper calibrated settings. Alternatively, the user/wearer can take an initial reading with the sensor and additionally take a near-simultaneous reading with another glucose sensor (e.g., a blood stick meter). This value from the other sensor would be input into the sensor with user input means such as knobs, buttons and the like connected to a microcontroller.

FIGS. 4A-4C shows actual data from an embodiment of the invention used to detect glucose concentrations of 75 mg/dL, 150 mg/dL, and 300 mg/DL. The left side of each example shows actual signals received from the polarized detector 28 and the non-polarized detector 30. The right side of each example shows the output of the subtractor circuit. The embodiment is calibrated for a baseline of 75 mg/dL. In FIG. 4A, the subtractor circuit averages to zero, indicating no change from the baseline. In FIG. 4B, the subtractor circuit averages to approximately 0.00005 Volts. In FIG. 4C, the output of the subtractor circuit averages to approximately 0.0001 Volts, or twice the middle example, which is expected give that the concentration of the bottom example is twice the concentration of shown in FIG. 4B.

FIGS. 5A-5C show the same data depicted in FIGS. 4A-4C, but with the unpolarized and polarized waveforms on the same graph. FIG. 5A corresponds to the data shown in FIG. 4A. FIG. 5B corresponds to the data shown in FIG. 4B. FIG. 5C corresponds to the data shown in FIG. 4C.

FIGS. 6A-C illustrate the operative effects of the feedback circuit 101. FIG. 6A depicts the linear relationship of the intensity of light received by a detector as represented by the mA of current conducted through a detector versus the mg/dL concentration of glucose. FIG. 6B illustrates the divergence of this linear relationship arising from uncompensated attenuation of the optical energy, whereas FIG. 6C shows the calibrating effect on this linear relationship arising from compensating for attenuation of the optical energy by a feedback circuit 101.

The present disclosure includes preferred or illustrative embodiments in which specific sensors and methods are described. Alternative embodiments of such sensors can be used in carrying out the invention as claimed and such alternative embodiments are limited only by the claims themselves. Other aspects and advantages of the present invention may be obtained from a study of this disclosure and the drawings, along with the appended claims. 

The invention claimed is:
 1. A noninvasive system for passing optical energy through a fluid-containing tissue to measure glucose concentration therein, the system comprising: a light source providing a first light; a polarizer receiving the first light and providing a second light, the first light and the second light being at least partially differently polarized; a first detector positioned to detect at least some or all of the first light; and a second detector positioned to detect at least some or all of the second light; the first detector configured to determine an intensity of a portion of the first light detected by the first detector; and a feedback circuit connecting the light source and the first detector and adjusting an amplitude of the light source to maintain the intensity of the portion of the first light detected by the first detector within a first portion calibration range, wherein (i) the light source and (ii) the first and second detectors are configured to receive the fluid-containing tissue between (i) the light source and (ii) the first and second detectors.
 2. The noninvasive system of claim 1, wherein the first portion calibration range is defined by an upper calibration threshold greater than a first target intensity value and a lower calibration threshold lesser than the first target intensity value.
 3. The noninvasive system of claim 1, further comprising a further polarizer between the light source and the polarizer and polarizing the first light, wherein polarizer and the further polarizer are differentially rotated.
 4. The noninvasive system of claim 1, further comprising a circuit, in which a first output from the first detector, and a second output from the second detector are each provided to the circuit, the circuit comprising a Wheatstone bridge for producing at least a third output as a difference between the first output and the second output.
 5. The noninvasive system of claim 1, further comprising a circuit at least one of increasing, decreasing, and comparing, a first output of the first detector and a second output of the second detector.
 6. A method for passing optical energy through a fluid-containing tissue to measure glucose concentration therein, the method comprising: positioning a polarizer to be illuminated by a light source, wherein the combination of the light source and the polarizer provides a first light and a second light, wherein the second light is polarized by the polarizer; positioning a first detector to detect at least some or all of the first light, the first detector providing a first output; positioning a second detector to detect at least some or all of the second light, the second detector providing a second output, wherein (i) the light source and (ii) the first and second detectors are configured to receive the fluid-containing tissue between (i) the light source and (ii) the first and second detectors; providing a feedback circuit connecting the light source and the first detector; and adjusting an amplitude of the light source to maintain an amplitude of the first output within a first portion calibration range; and comparing a magnitude of the first output and the second output to determine a relative intensity of the first light relative to the second light or the second light relative to the first light.
 7. The method of claim 6, wherein the comparing the magnitude comprises providing a circuit for receiving the first output and the second output, the circuit comprising at least a subtractor for producing at least a third output as a difference between the first output and the second output, a compensator for boosting at least a portion of the second output, and a gain to amplify at least the third output.
 8. A noninvasive system for passing optical energy through a fluid-containing tissue to measure glucose concentration therein, the system comprising: a polarizer for receiving a first light, whereby there is created, from the first light, a second light polarized differently than the first light; a first detector positioned to detect first light; and a second detector positioned to detect second light; a feedback circuit configured to interconnect a source of the first light to the first detector and configured to adjust an intensity of the first light to maintain the at least some or all of the first light detected by the first detector within a first portion calibration range; and one or more of the first detector and the second detector being so adjusted that the first light to the first detector is of a similar intensity as that of the second light to the second detector, wherein (i) the light source and (ii) the first and second detectors are configured to receive the fluid-containing tissue between (i) the light source and (ii) the first and second detectors. 